Effect of Diel Cycling Temperature, Relative Humidity, and Synthetic Route on the Surface Morphology and Hydrolysis of α-U₃O₈

Abstract

The speciation and morphological changes of α-U 3 O 8 following aging under diel cycling temperature and relative humidity (RH) have been examined. This work advances the knowledge of U-oxide hydration as a result of synthetic route and environmental conditions, ultimately giving novel insight into nuclear material provenance. α-U 3 O 8 was synthesized via the washed uranyl peroxide (UO 4 ) and ammonium uranyl carbonate (AUC) synthetic routes to produce unaged starting materials with different morphologies. α-U 3 O 8 from UO 4 is comprised of subrounded particles, while α-U 3 O 8 from AUC contains blocky, porous particles approximately an order of magnitude larger than particles from UO 4 . For aging, a humidity chamber was programmed for continuous daily cycles of 12 "high" hours of 45 °C and 90% RH, and 12 "low" hours of 25 °C and 20% RH. Samples were analyzed at varying intervals of 14, 24, 36, 43, and 54 days. At each aging interval, crystallographic changes were measured via powder X-ray diffraction coupled with whole pattern fitting for quantitative analysis. Morphologic effects were studied via scanning electron microscopy and 12-way classification via machine learning. While all samples were found to have distinguishing morphologic characteristics (93.2% classification accuracy), α-U 3 O 8 from UO 4 had more apparent change with increasing aging time. Nonetheless, α-U 3 O 8 from AUC was found to hydrate more quickly than α-U 3 O 8 from UO 4 , which can likely be attributed to its larger surface area and porous starting material morphology.

Equilibrium Fractionation of Oxygen Isotopes in the U3O8–Atmospheric Oxygen System

“…U 3 O 8 has different types of oxygen bonded to uranium, yielding different bond lengths. At room temperature (orthorhombic structure), two uranium atoms [labeled U(1) and U(2)] are surrounded by six oxygen atoms at distances between 2.07 and 2.23 Å, with the seventh oxygen atom bonded to U(1) and U(2) at distances of 2.44 and 2.71 Å, respectively. − Loopstra established that the room-temperature orthorhombic and high-temperature hexagonal structures are similar, except that the hexagonal structure has one uranium site, whereas the orthorhombic structure has two. However, the surrounding oxygens are approximately equivalent for both lattice types …”

Tailoring Triuranium Octoxide into Multidimensional Uranyl Fluoride Micromaterials

“…U 3 O 8 microplates have already been reported and were formed from the thermal decomposition of uranyl ammonium carbonate. − U 3 O 8 mp reported here could be used as precursors to prepare several other uranium oxide materials (UO 2 , UO 3 ) with a rectangular geometry, enabling investigations on the effects of morphology (i.e., mp vs ms) of uranium oxides on several physicochemical properties (i.e., catalysis).…”

In Situ Liquid Cell Transmission Electron Microscopy Study of Studtite Particle Formation and Growth via Electron Beam Radiolysis

“…Controlling particle morphology is of great importance to many industries including semiconductors, nanomaterials, and steel fabrication. − Levlev et al showed that a mechanistic understanding of nucleation and growth mechanisms can lead to improved modeling of material properties and future material discovery . In the nuclear industry, particle morphology can impact the environmental transport of uranium, nuclear fuel performance in reactors, long-term storage of spent nuclear fuel, and support nuclear forensics and nuclear safeguards in identifying the processing history of nuclear materials. ,, Prior studies have identified many variables including pH, temperature, reaction time, and calcination temperature that impact the final particle morphology. − Advancements in particle segmentation and machine learning enable quantification of even subtle morphology changes. , The challenge, however, has been in understanding the fundamental principles that result in unique particle morphologies based on the chemical and physical processing conditions. In situ liquid phase transmission electron microscopy can help reveal the underlying mechanisms of particle formation, particularly when the impacts of radiolysis can be mitigated. , In the case of studtite, electron beam radiolysis of uranyl solutions enables the controlled in situ precipitation of particles under different reaction conditions.…”